A syringe is used in dentistry for controlled delivery of liquid, air, or a combination of liquid and air, to the mouth of the patient. A syringe generally includes a syringe head that is manipulated by the operator and connected by flexible conduits to a source of water and compressed air. A tubular, elongated syringe tip is connected to the syringe head.
A conventional syringe tip comprises an inner tube and a concentric outer tube. The inner tube mates at one end with a liquid-outlet port in the syringe head, thereby providing a conduit for the liquid from the syringe head to the free end of the syringe tip.
The outer tube of the syringe tip has an inside diameter that is slightly greater than the outside diameter of the inner tube, thereby defining between the inner and outer tubes an annular air delivery chamber extending along the length of the syringe tip. The outer tube of the syringe tip joins the inner tube at the tip end that connects to the syringe head. At that end, the air delivery chamber is substantially closed, except for an air-inlet port in the outer tube that connects that chamber with an air-outlet port in the syringe head. Air flows out of the air delivery chamber at the free end of the syringe tip.
The operator controls the flow of liquid or gas through the syringe tip by operating valves that are mounted in the syringe head.
Syringe tips are disinfected after use with a single patient. Consequently, the mechanism employed for connecting the syringe tips to a syringe head should provide for quick and simple replacement of syringe tips while ensuring an effective seal between the syringe head and the connected syringe tip.
FIGS. 1 and 2 depict a prior art syringe tip assembly 10 for connecting a syringe tip 20 to a conventional syringe head 22. The syringe head 22 includes a threaded aperture 24, the innermost end of which aperture is in a fluid communication with a liquid-outlet port 26 and an air-outlet port 28 formed in the head 22. The liquid-outlet port 26 is connected to a flexible conduit (not shown) that extends from the syringe head 22 to a source of liquid, such as water. Similarly, the air-outlet port 28 is connected to a flexible conduit that connects the syringe head 22 with a source of compressed air. The liquid-outlet port 26 and the air-outlet port 28 are opened and closed by internal valves. A three-position button 30 is manipulated by the operator to control the valves.
The syringe tip 20 includes an elongated inner tube 32 and a concentric outer tube 34. The syringe tip 20 has a connecting end 36 that connects to the syringe head 22, and a free end 38 from which the liquid and air are expelled.
The connecting end 36 of the syringe tip fits into one end of a generally tubular coupler 40. The coupler 40 has near its innermost end 42 a threaded portion 44 that threads into the threaded aperture 24 in the syringe head 22.
At the connecting end 36 of the syringe tip 20, the inner tube 32 protrudes from the outer tube 34 to fit within the liquid-outlet port 26 in the syringe head. An annulus 46 is formed to protrude from the innermost end 42 of the coupler 40. An O-ring 48 fits inside the annulus 46. The annulus 46 and O-ring 48 are sized so that the O-ring 48 is firmly compressed against the syringe head 22 and around the portion of the inner tube 32 that protrudes from the outer tube 34 (FIG. 2). The O-ring 48, therefore, seals the connection between the liquid-outlet port 26 and the inner tube 32.
The end 66 of the coupler 40 that is opposite the annulus 46 carries external threads 50 for receiving a retainer nut 52 through which nut the syringe tip 20 extends as described below. A smooth portion of the exterior wall of the coupler 40 between the threaded portions 44, 50 carries an O-ring 54 for sealing the annular space between the retainer nut 52 and syringe head 22 whenever the nut 52 is tightened to the coupler 40.
The retainer nut 52 is a hollow, generally frustum shaped member having an inner end 56 and an outer end 58. The interior of the inner end 56 of the retainer nut 52 is threaded to engage the threads 50 on the coupler 40. Part of the outer surface of the inner end 56 is hexagonal in cross-section to receive a wrench for tightening the retainer nut 52 to the coupler 40.
Whenever the retainer nut 52 is tightened to the coupler 40 with the connecting end 36 of the syringe tip 20 in place (FIG. 2), a locking O-ring 60, which fits inside the retainer nut 52, is firmly compressed between a tapered sleeve 64 and the outer end 66 of the coupler 40 so that the locking O-ring 60 is forced into an annular recess 62 formed in the outer surface of the outer tube 34.
More particularly, the outer surface 67 of the tapered sleeve 64 tapers outwardly (i.e., to the left in FIG. 2) and bears against a correspondingly tapered surface 68 defined by the inside wall of the retainer nut 52. The locking O-ring 60 is located between the tapered sleeve 64 and the outer end 66 of the coupler 40. As a result, whenever the retainer nut 52 is threaded onto the coupler 40, the tapered sleeve 64 is forced against the locking O-ring 60, compressing the ring 60 as mentioned above, thereby securing the syringe tip 20 to the coupler 40 (hence, to the syringe head 22).
The outer tube 34 is crimped to the inner tube 32 at connecting end 36 to close the end of the air delivery chamber 70 that is defined between the outer tube 34 and the inner tube 32. An annular recess 72 is formed near the crimped end. Two or more inlet ports 74 are formed through the outer tube 34 at the recess 72. An air passage 75 is defined between the outer surface of the tube 34 and the inner wall 76 of the coupler 40 at the crimped end of the outer tube 34. This air passage 75 is in fluid communication with the air-outlet port 28 in the syringe head 22 via holes 78 in the innermost end 42 of the coupler 40.
The just described prior art syringe tip assembly 10 is designed so that the retainer nut 52 must be securely fastened to the coupler 40 in order to retain the syringe tip 20 in place. Accordingly, it is necessary to employ a tool for loosening the retainer nut 52 to permit removal of the syringe tip 20. In loosening the retainer nut 52, the nut may be backed completely off the threads 50 of the coupler 40, which can lead to the separation and loss of internal parts, such as the tapered sleeve 64 and the locking O-ring 60.
In some dental procedures it is desireable to secure the tip 20 to the syringe head 22 so that it is irrotatable about its longitudinal axis. Such an irrotatable syringe tip may be desirable, for example, when the tip 20 is used for retracting the cheek of a patient. The tip must be secured against rotation because the retraction force applied to the bent free end of the tip 20 tends to rotate the tip within the coupler 40. The prior art syringe tip assembly 10 just described is designed so that the compressed locking O-ring 60 normally secures the tip 20 to be irrotatable about its longitudinal axis.
In other applications, a rotatable syringe tip is preferred. The tip 20 can be made rotatable by loosening the retainer nut 52, thereby permitting the locking O-ring 60 to resile and reduce the force applied by the O-ring to the outer tube 34. By loosening the retainer nut 52, however, it is possible that subsequent rotation of the syringe tip 20 will be transferred via the O-ring 60 to the retainer nut 52, which can eventually unthread the retainer nut 52 and cause the tip 20, retainer nut 52, and internal parts to fall from the syringe head 22.
In the past, split collets have been available for replacing the tapered sleeve 64 mentioned above. The force of the retainer nut interior surface 68 against the split collet tightens the collet 64 to the tip 20 to restrict tip rotation. The collet, however, may be lost in the event that the retainer nut 52 is loosened as described above.
This invention is directed to an assembly for connecting a syringe tip to a syringe head and provides for rapid replacement of the syringe tip. In many applications, the need for a tool to loosen the connection is eliminated.
The assembly is adjustable for permitting or prohibiting rotation of the syringe tip about its longitudinal axis. In one embodiment, the assembly is configured so that rotation of the tip can not unthread the retainer nut from the coupler. In another embodiment, the assembly is configured so that individual components (collet and O-rings) are not free to fall from the coupler even though the retainer nut is removed.
As another aspect of this invention, the assembly is constructed so that it may be used with existing syringe heads.